This invention relates to communications systems, and more particularly to setting automatic gain control during signal acquisition, while transitioning from an overhead segment to data-bearing segment.
In select modes of operation of communication systems there exists the need to rapidly set the automatic gain control (AGC) setting while performing other overhead functions, such as during signal acquisition. In addition, the signal often changes its structure when transitioning from the overhead segment to the data-bearing segment.
As an example, consider a packet communication system that has an acquisition header section modulated using the binary-phase-shift-key (BPSK) formal and a data bearing section modulated using the quadrature-amplitude-modulation (QAM) format. In general, the AGC setting attained during the BPSK modulation signal segment has to change during the QAM signal segment due to the differences in signal structure between the two signal segments. A gain transient is introduced at the boundary of the two signal segments that impairs the system performance bit error rate (BER) during the duration of the transient.
A general object of the invention is to set an automatic gain control during signal acquisition.
Another object of the invention is to set an automatic gain control from a header, of a packet, using binary-phase-shift-key modulation and maintain the setting for data, in the packet, using quadrature-amplitude modulation.
According to the present invention, as embodied and broadly described herein, a packet transmitter for communicating data in a plurality of packets is provided. Each packet has at least a first signal segment and a second signal segment. Each signal segment is characterized by a different modulation format. The first signal segment, by way of example, might have binary-phase-shift-keying (BPSK) modulation and serve as a header for synchronization. The second signal segment might have quadrature amplitude modulation (QAM) and contains data.
The invention includes a mapping circuit, or other equivalent device, for mapping the first signal segment and the second signal segment between an address port, or equivalent signal input port, and an output port, so that some statistic of the second signal segment, such as the average power level, or probability of error, of the second signal segment, is the same statistic of the first signal segment, such as the average power level, or probability of error, of the first signal segment. The mapping circuit also includes an input port for inputting mapping characteristics of the first signal segment and mapping characteristics of the second signal segment. The mapping characteristics of each signal segment, be they for the first signal segment, the second signal segment or for a plurality of signal segments, are designed so that the average power level of the first signal segment, of the second signal segment or of a plurality of signal segments is the same.
The mapping circuit typically might be used with a transmitter having a plurality of data channels at an input, and the plurality of data channels are spread-spectrum processed and combined as a multilevel signal. The multilevel signal gives rise to variable output power levels when compared to a continuous wave signal having BPSK modulation.
Additional objects and advantages of the invention are set forth in part in the description which follows, and in part are obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention also may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.